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First published online August 26, 2005; 10.1104/pp.105.065904 Plant Physiology 139:363-374 (2005) © 2005 American Society of Plant Biologists Cassava Plants with a Depleted Cyanogenic Glucoside Content in Leaves and Tubers. Distribution of Cyanogenic Glucosides, Their Site of Synthesis and Transport, and Blockage of the Biosynthesis by RNA Interference Technology1Plant Biochemistry Laboratory, Department of Plant Biology, Center for Molecular Plant Physiology (K.J., S.B., P.K.B., C.S., B.L.M.), and Chemistry Department (C.E.O.), Royal Veterinary and Agricultural University, DK–1871 Frederiksberg C, Copenhagen, Denmark; and Laboratory of Plant Biotechnology, Swiss Federal Institute of Technology, Eidgenössische Technische Hochschule Zentrum, CH–8092 Zurich, Switzerland (J.P.-K.)
Transgenic cassava (Manihot esculenta Crantz, cv MCol22) plants with a 92% reduction in cyanogenic glucoside content in tubers and acyanogenic (<1% of wild type) leaves were obtained by RNA interference to block expression of CYP79D1 and CYP79D2, the two paralogous genes encoding the first committed enzymes in linamarin and lotaustralin synthesis. About 180 independent lines with acyanogenic (<1% of wild type) leaves were obtained. Only a few of these were depleted with respect to cyanogenic glucoside content in tubers. In agreement with this observation, girdling experiments demonstrated that cyanogenic glucosides are synthesized in the shoot apex and transported to the root, resulting in a negative concentration gradient basipetal in the plant with the concentration of cyanogenic glucosides being highest in the shoot apex and the petiole of the first unfolded leaf. Supply of nitrogen increased the cyanogenic glucoside concentration in the shoot apex. In situ polymerase chain reaction studies demonstrated that CYP79D1 and CYP79D2 were preferentially expressed in leaf mesophyll cells positioned adjacent to the epidermis. In young petioles, preferential expression was observed in the epidermis, in the two first cortex cell layers, and in the endodermis together with pericycle cells and specific parenchymatic cells around the laticifers. These data demonstrate that it is possible to drastically reduce the linamarin and lotaustralin content in cassava tubers by blockage of cyanogenic glucoside synthesis in leaves and petioles. The reduced flux to the roots of reduced nitrogen in the form of cyanogenic glucosides did not prevent tuber formation.
1 This work was supported by the Danish International Development Agency (grant nos. 104Dan8/503 and 104.Dan.8/91125) and by a grant to the Center for Molecular Plant Physiology (PlaCe) from the Danish National Research Foundation. 2 Present address: Virology and Molecular Toxicology, Novo Nordisk A/S, Novo Nordisk Park, 2760 Malov, Denmark. 3 Present address: European Patent Office, Directorate 2.4.01 Biotechnology, EPA/EPO/OEB, D–80298 Munich, Germany. Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.065904. * Corresponding author; e-mail blm{at}kvl.dk; fax 45–35–28–33–33. Received May 19, 2005; returned for revision June 28, 2005; accepted June 29, 2005. This article has been cited by other articles:
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